ADS-B (Automatic Dependent Surveillance Broadcast) is an aircraft status signal. ADS-B messages are transmitted by aircraft via low power radio frequency signals and contain information as for example the aircraft position, altitude, or velocity. They are unencrypted and publicly available for everybody with a compatible receiver.
ADS-B is an enabler for enhanced airspace surveillance; for instance it is used to avoid air collisions and facilitates air traffic control operations. However, in order to achieve and maintain a consistent quality, reliability and availability of surveillance across all phases of flight, a single source ADS-B tracking may not be adequate.